.TH std::ranges::crend 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::ranges::crend \- std::ranges::crend

.SH Synopsis
   Defined in header <ranges>
   Defined in header <iterator>
   inline namespace /* unspecified */ {

       inline constexpr /* unspecified */ crend = /*       \fI(since C++20)\fP
   unspecified */;                                         (customization point object)

   }
   Call signature
   template< class T >

       requires /* see below */                            \fI(since C++20)\fP

   constexpr /* see below */ auto crend( T&& t );

   Returns a sentinel
   for the constant iterator
   (since C++23) indicating the end of a
   const-qualified
   (until C++23) range that is treated as a reversed sequence.

   range-rbegin-rend.svg

   Let CT be

     * const std::remove_reference_t<T>& if the argument is an lvalue (i.e. T is
       an lvalue reference type),                                                (until
     * const T otherwise.                                                        C++23)

   A call to ranges::crend is expression-equivalent to
   ranges::rend(static_cast<CT&&>(t)).
   If the argument is an lvalue or
   ranges::enable_borrowed_range<std::remove_cv_t<T>> is true, then a call to
   ranges::crend is expression-equivalent to:

     * std::const_sentinel<decltype(U)>(U) for some expression U equivalent to   (since
       ranges::rend(/*possibly-const-range*/(t)).                                C++23)

   In all other cases, a call to ranges::crend is ill-formed, which can result
   in substitution failure when the call appears in the immediate context of a
   template instantiation.

   If ranges::crend(e) is valid for an expression e, where decltype((e)) is T, then
   CT models std::ranges::range, and
   (until C++23) std::sentinel_for<S, I> is true in all cases, where S is
   decltype(ranges::crend(e)), and I is decltype(ranges::crbegin(e)).
   Additionally, S models constant-iterator if it models input_iterator.
   (since C++23)

  Customization point objects

   The name ranges::crend denotes a customization point object, which is a const
   function object of a literal semiregular class type. For exposition purposes, the
   cv-unqualified version of its type is denoted as __crend_fn.

   All instances of __crend_fn are equal. The effects of invoking different instances
   of type __crend_fn on the same arguments are equivalent, regardless of whether the
   expression denoting the instance is an lvalue or rvalue, and is const-qualified or
   not (however, a volatile-qualified instance is not required to be invocable). Thus,
   ranges::crend can be copied freely and its copies can be used interchangeably.

   Given a set of types Args..., if std::declval<Args>()... meet the requirements for
   arguments to ranges::crend above, __crend_fn models

     * std::invocable<__crend_fn, Args...>,
     * std::invocable<const __crend_fn, Args...>,
     * std::invocable<__crend_fn&, Args...>, and
     * std::invocable<const __crend_fn&, Args...>.

   Otherwise, no function call operator of __crend_fn participates in overload
   resolution.

.SH Example


// Run this code

 #include <algorithm>
 #include <iostream>
 #include <iterator>
 #include <vector>

 int main()
 {
     int a[]{4, 6, -3, 9, 10};
     std::cout << "Array backwards: ";
     namespace ranges = std::ranges;
     ranges::copy(ranges::rbegin(a), ranges::rend(a),
                  std::ostream_iterator<int>(std::cout, " "));
     std::cout << '\\n';

     std::cout << "Vector backwards: ";
     std::vector v{4, 6, -3, 9, 10};
     ranges::copy(ranges::rbegin(v), ranges::rend(v),
                  std::ostream_iterator<int>(std::cout, " "));
     std::cout << '\\n';
 }

.SH Output:

 Array backwards: 10 9 -3 6 4
 Vector backwards: 10 9 -3 6 4

.SH See also

   ranges::rend returns a reverse end iterator to a range
   (C++20)      (customization point object)
   rend         returns a reverse end iterator for a container or array
   crend        \fI(function template)\fP
   \fI(C++14)\fP
